1. Field of the Invention
The present invention relates to an improved process for producing alkoxy-substituted triphenylamines.
The alkoxy-substituted triphenylamines obtained by the process of the present invention are useful compounds as an intermediate for use in general chemical industries, particularly as an intermediate for dyes, agricultural chemicals, rubber chemicals and the like.
2. Description of the Related Art
It has hitherto been known to prepare triphenylamines by reacting cyclohexanones with diphenylamines, while forming the cyclohexanones in the same system from phenols used as the hydrogen acceptor in the presence of a hydrogen transfer catalyst (Japanese Patent Laid-Open No. 183250/1986). The reference describes that triphenylamine is obtained in an yield of 68.5% (selectivity: 85.1%) by reacting diphenylamine with cyclohexanone in an excess amount of phenol in the presence of a palladium catalyst.
However, when the present inventors traced the above-described process by using an alkoxy-substituted cyclohexanone and an alkoxy-substituted phenol as raw materials, they found that a triphenylamine with the alkoxy substituent eliminated was by-produced in a considerable amount, but an alkoxy-substituted triphenylamine, the desired product, could not be obtained in a satisfactorily high yield.